I’ve gotten glimmer fast by performing missions in PvE. Any extra loot and crates scattered in the map often have glimmer between +125 - +135. Any spare guns you find can be dismantled for gun parts and glimmer. When dismantled they range from +6 - +15 a piece depending on the power of the weapon and rarity. Specifically, when you get the item called “Ether Seeds” which is dropped on missions. Those items provide a boost and with every enemy killed, they will drop extra glimmer for 10 minutes. So when I get that kind of item, I then go through a Strike mission so I can rack up kills and money at the same time.